nginx.pid的作用：记录nginx的main process的pid，方便kill的调用；（因为调用kill需要提供pid）
请求uri：请求uri是不包含query string的uri，比如http://localhost:8080/test/a=1的请求uri指的是/test；nginx通过请求uri和location进行匹配
location的正则：其实正则就是perl规范的，只是location的正则需要以~或~*开头
location匹配规则：所有可以匹配的location中，先选有正则的location，其次再选最长的location；[ = | ~ | ~* | ^~ | @]是可以包含的前缀，各自的意义见nginx配置location - 简书 (jianshu.com)
When nginx selects a
locationblock to serve a request it first checks location directives that specify prefixes, rememberinglocationwith the longest prefix, and then checks regular expressions. If there is a match with a regular expression, nginx picks thislocationor, otherwise, it picks the one remembered earlier.
